Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $9.80   3.357%   $10.129   $10.13   $10.15   $10.10  
  Purchase #2 $60.72   11.686%   $67.8157   $67.82   $67.80   $67.80  
  Purchase #3 $67.96   12.816%   $76.6698   $76.67   $76.65   $76.70  
  Purchase #4 $9.57   4.491%   $9.9998   $10.00   $10.00   $10.00  
  Purchase #5 $211.26   3.327%   $218.2886   $218.29   $218.30   $218.30  
  Purchase #6 $189.50   13.741%   $215.5392   $215.54   $215.55   $215.50  
  Purchase #7 $203.70   4.285%   $212.4285   $212.43   $212.45   $212.40  
  7 purchase totals = $752.51       $810.8706   $810.88   $810.90   $810.80